Assemblies of this type serve to designate a target by means of a laser emitter (generally a telemeter) whose radiation (which is generally infrared radiation) is directed by an operator towards the target which the operator observes and tracks by the optical aiming means. More generally, a collimator is provided suitable for forming a visible image of a reticle which represents the aiming direction and which is superposed on the image of the target, such that the reference direction (i.e. the direction in which the laser telemeter is pointing) coincides with the aiming direction when the image of the target is placed in the middle of the reticle.
When a projectile is fired at the target, the radiation of its tracer is received and directed to an angle measuring device (also referred to herein as "localization means"). The angle measuring device also receives a signal representative of the direction to the target, thus defining a "localization direction" which is the direction in which the localizing means "imagines" the target to be found (except for the case in which a laser emitter also serves as an illuminator no radiation returned from the target is directly available to the localization means). The relative position in three dimensions between the two input directions is determined and the localization means derives an angular difference signal representative of the angular difference between the direction to the projectile and the localization direction (which ideally coincides with the direction to the target as designated by the laser beam, i.e. with the reference direction). This information can subsequently be used to remotely control the projectile so that its trajectory is directed to the target direction.
Further, the laser emitter generally co-operates with telemetry means which additionally receive the radiation reflected from the target in order to derive a telemetry signal representative of the distance to the target and, where applicable, a signal representative of the relative speed of the target, said data being derived from the propagation time of the return laser pulse.
One of the difficulties encountered with this type of device lies in ensuring that the reference or aiming direction (i.e. the real direction to the target), the direction indicated by the collimator reticle (hereinafter designated "the collimator direction" which is the apparent direction to the target as seen by the eye of the operator), and the localization direction (which is the theoretical direction to the target as taken into consideration by the localization means) all coincide. When the operator aims at a target, it is essential that the center of the reticle corresponds very exactly with the reference and localization directions. If this condition is not satisfied the distance-measuring and angle-measuring means will be operating on a point which differs to a greater or lesser extent from the point occupied by the target.
Techniques for performing this adjustment or "harmonization" already exist in the prior art.
When the aiming is performed by purely electronic means (with the aiming field being projected onto a flying spot cathode tube or the like, and with the target being automatically tracked), it is possible to perform such harmonization by modifying the flying spot scan. One such harmonization technique is described, for example, in published French patent specification No. 2 475 208.
The present invention is concerned with the case where aiming is performed by purely optical means using a reticle, i.e. where it is the operator himself who designates the target by centering it in the collimator and who tracks the target in his field of view.
In such a case, the difficulty is increased by the fact that the distance-measuring and angle-measuring assembly (which is an electronic assembly) and the aiming assembly (which is a purely optical assembly) constitute two separate blocks. Harmonization is generally performed by very fine adjustment of the angular position of the beam emitted by the telemeter relative to the aiming block which transmits the beam, thereby presupposing accurate adjustment means and a very rigid mechanical structure for avoiding subsequent loss of alignment.